ESP32 SMS-to-Cloud Gateway
ESP32‑powered gateway that listens for incoming SMS on a SIM800L module and forwards them to Discord, Telegram, and Gmail in real time over secure Wi‑Fi.
This project started as a simple experiment with a SIM800L GSM module and turned into a handy little device that bridges old‑school SMS with modern chat platforms. The ESP32 sits in the middle, listens for new text messages, and instantly forwards them to Discord, Telegram, and email.
What It Does
When the SIM800L receives an SMS, the ESP32 picks it up, reads the sender and message, and sends it out to my chosen platforms:
• A Discord webhook posts the message in my server in real time. • A Telegram bot DM's me the same message. • The message is emailed through Gmail's SMTP server using secure SSL.
Everything runs over Wi‑Fi with proper TLS/SSL encryption and verified root certificates, so it's fully secure end to end.
How It Works
The ESP32 talks to the SIM800L over serial, checks for new messages, and uses a simple queue to handle multiple SMS deliveries smoothly. I wrote the firmware in Arduino C++, built around HTTPClient and WiFiClientSecure, and added plenty of serial debug output to make troubleshooting easy.
The device can run on either a classic ESP32 Dev Module or the smaller ESP32‑C3 SuperMini. It only needs a stable 5 V supply and a healthy GSM signal.
Issues
The main real-world limitation for this build isn’t the code or wiring—it’s the carrier. Many service providers block or restrict IoT and non‑phone hardware on consumer SIM plans. A module like the SIM800L often gets classified as an unknown or unsupported device, so activation, SMS, or data simply never works reliably even when the firmware is fine.
Cricket Wireless is a concrete example: they publish a specific list of phones on their website that their SIM is certified to work with. That policy effectively excludes random IoT boards—Cricket is geared toward those handsets, not maker modules—so a SIM that works in a supported phone may still fail in this gateway.
If you recreate something like this, plan on testing carriers and plans that explicitly allow IoT, M2M, or modem‑style use (or a SIM intended for embedded gateways), not only “whatever cheap prepaid SIM fits.”
Why I Built It
I wanted a lightweight way to forward important SMS notifications—bank alerts, IoT sensor messages, or SIM‑based devices—to platforms I actually check every day. Now I get messages instantly, no matter where they come from, and I can log them all through Discord or my inbox.
Highlights
- Secure HTTPS and SMTP with verified root certificates
- Real‑time cross‑platform message delivery
- Works with both ESP32 and ESP32‑C3 boards
- Modular design ready for OTA updates and new APIs
- Built entirely with affordable, maker‑grade parts